<?php
//$arr = [1,2,3,4];
//
//foreach ($arr as $k => &$a){
//    echo $a;
//}
//
//echo "开始<br>";
//foreach ($arr as $k =>$a){
//    echo $a;
//    print_r($arr);
//}
$a = 10;
$b = &$a;
unset($a);
echo $b;
echo $a;